Fluid conduit systems have tropically been made of ferrous metals. The metal conduit is generally provided in fixed lengths and is cut to size prior to installation. The metal conduit is then threaded in the field and mated with a coupling. The installation of such pipe is cumbersome, time intensive and expensive. Copper pipes install more quickly than ferrous metal pipes but are also more expensive than ferrous metal pipes.
Plastic pipe has also been used in fluid conduit systems. Plastic pipe can be less expensive than either ferrous metals or copper pipes. However, the plastic pipes are more flexible than either copper pipes or ferrous metal pipes and therefore need more support. The additional support necessary adds to the installation time and material costs of the entire system.
Hybrid plastic/metal pipes and fittings have been proposed for fluid conduit systems for many years. For example, U.S. Pat. No. 4,216,802 discloses a deformable composite pipe product. The product comprises a seamless inner tubular shaped layer made from a polymeric layer. The metallic material is preferably made from an alloy of copper or aluminum. The outer layer can be selected from a variety of thermoplastically processable materials such as for example rubber, nylon, thermoplastic rubber, polyurethane and the like. Preferably, the outer layer is a thermoplastically processable semicrystalline polymer such as polyvinyl chloride or a high density polyethylene composite. The polymeric material may be cross-linked to improve the properties of the composite pipe. The outer layer is preferably formed around the inner layer by means of an extrusion process. The inner and outer layers are bonded together by means of a polyamide based hot melt adhesive interposed between the two layers. The outer diameter of the outer layer is sized so that the composite tubing product can be attached without further dimensional alteration to fittings generally used to couple equivalently dimensioned pipes having a singular polymeric or metallic wall.
A three layer flexible pipe is described in European Patent Application 0 084 088 A 1. The inside layer of this pipe is made of a heat resistant material such as perfluoroethylene propylene or polyvinylidene fluoride. The intermediate layer is a metal foil such as aluminum, whereas the thicker outer layer is made of an extruded polyamide, polypropylene or a polyethylene-propylene mixture or a cross-linked polyethylene; all of which are semi-crystalline thermoplastic polymers.
A semi-rigid plastic tube with a integral metallic tubular reinforcement is described in European Patent Application 0 067 919 A1 . The semi-rigid, semi-crystalline plastic tube can be made oDf a polyolefin, polyamide or polyamide resin. The tube is enclosed by a layer of aluminum metal or alloy, which layer is welded using a laser. The external layer is an extruded layer.
European Patent Application 0 230 457 A1 discloses a composite fuel and vapor tube. The composite tube is a bendable tubular article for transport of fuels which comprises a bendable metal strip formed sleeve extending throughout the length of the article and having an adhesive layer on the other surface of the metal sleeve. A flexible plastic jacket encases the metal sleeve. Additionally, the metal sleeve has a flexible bendable tubular liner that is made of petroleum resistant materials. The metal sleeve used in the invention is preferably aluminum. The metal sleeve offers sufficient strength to dominate over the resiliency of the plastic layer when the tubing is bent to a desired configuration.
Similarly, European Patent Application 0 639 411 A1 discloses a process for manufacturing a composite tube with two or more layers of different materials. The tube preferably comprises three layers with metal sandwiched between the plastic layers, such as polyethylene or cross-linked polyethylene; both of which are semi-crystalline materials.
European Patent 0 154 931 A1 describes a composite pipe made by wrapping an extruded plastic pipe with a ductile metal sheet to form a continuous tube. The metal sheet is butt welded before it is enclosed by a further extruded plastic sheath or tube. An adhesive may be placed between the metal sheet and the outer plastic sheath. The inner extruded plastic pipe is a cross-linked polyolefin, fluorinated polymer, polyamide or an elastomer. The metal sheet used in the composite pipe is aluminum or an alloy of aluminum; whereas the adhesive is a ionomer, ethylene vinyl acetate or a modified polyethylene. This composite pipe can be shaped using bending tools. Furthermore, the pipe can be used at pressures up to 300 bars.
European Patent 0 237 234 A1 to Yasuo discloses a method of producing a composite pipe made of metal in which the inner surface of the metal hs covered by a plastic layer. According to this patent, a coiled metal sheet is formed into a cylinder. Molten resin is extruded into a cylindrical shape over the inner surface of the cylinder made from the metal. Generally, the liner is made from a fluororesin or aromatic polyester resin. In a preferred embodiment, the liner is made from a polyolefin compound in which the polyolefin is cross-linked by both hydrolysis and a radical reaction. The metal sheet is made from an aluminum alloy.
U.S. Pat. No. 4,559,973 discloses a water impervious heat shrinkable tube. The tube comprises an inner and outer layer plastic layers forming a tube and a laminated metal foil layer interposed between the inner and outer layers. The metal foil layer has a thickness of 0.1 mm. The plastic material to be laminated on both sides of the metal foil film is selected from the group consisting of polyethylene, polyvinyl chloride, saturated polyester, cross-linked polyethylene, ethylene-propylene rubber, silicon rubber, chloroprene rubber and fluoroplastic.
Similarly, International Patent Application WO/96/18840 discloses a conduit made of a multilayer material which is intended to convey a motor vehicle fluid. The conduit comprises an internal layer, an intermediate layer and an external layer. The intermediate layer comprises a thin sheet material, such as aluminum with the thickness of approximately 10-70millimicrons. In one example, the internal layer is a polyamide pipe and the outer layer is cross-linked polyvinyl chloride.
Hybrid structures have also been proposed for fittings. For example, U.S. Pat. No. 5,143,407 to Cokeh discloses a pipe coupling device comprising a cylindrical outer layer of plastic formed with a central inwardly extending boss which coaxially supports a copper pipe extending there through and having recesses encircling the copper pipe adjacent each end of the outer layer to permit pipe to be coupled to be inserted into said recesses in a manner to encircle the copper pipe and to facilitate the joining of the pipe coupled to the outer layer. If desired, annular rubber washers are inserted into the recesses adjacent each end of the boss to provide a better seal.
U.S. Pat. No. 4,277,091 discloses a coupling joint for interconnecting the ends of metal conduit sections having plastic liners to form a continuously lined conduit and the method for making such joints. An open faced collar is used to join the ends of pipe sections to form a continuously lined conduit. The open face collar comprises an open ended cylindrical body, the outer dimensions of which substantially conform to the internal dimensions of the liner in the pipe. The open faced collar includes a radically extending flange which radiates outwardly from the end of the body to mate with the exposed face of the pipe. The open face collar is bonded to the pipe with a solvent such as methyl ethyl ketone or any suitable conventional epoxy cement. An identical open face collar is positioned within the open end of a section of a second pipe. If desired, a solvent or bonding agent may be applied to the flanges immediately prior to the assembly of the coupling to provide a sealing bond. The ends of the pipe sections to be joined are arranged coaxially with a coupling sleeve. The coupling sleeve is a relatively short section of a metal pipe having an internal diameter slightly less than the external diameter of the ends of the pipe section. The open ends of the coupling sleeve are preferably flared outwardly to aid in the insertion of the pipe sections. In the preferred embodiment:, the coupling sleeve is provided with a centrally located annular recess or groove which carries a sealing band. The sealing band is preferably the same material as the liner and open face collar and is bonded or secured within the recess by an epoxy binder or the like.
Despite many variations of hybrid and composite pipes and fittings, all of these pipes are deficient in that they do not balance the properties of both metal pipes and plastic pipes. A need still exists for a rigid, pressure bearing, impact resistant, multilayer thermoplastic composite pipe which can be easily installed. There is a great need for a multilayer composite pipe that balances both the properties of metal pipes and plastic pipes. Furthermore, a need exists for a fluid conduit system in which such a multilayer composite pipe can be used.